Tablets & Capsules


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This article describes how to conduct common com- pression studies, including how to develop profiles of tabletability, compactibility, and compressibility. Those terms—which are commonly misused—have specific meanings and offer different ways to characterize the material under compression. There are many factors that influence successful tablet manufacture, including a properly trained staff, a tablet press engineered for your product's specifications, high- quality and precisely machined compression tooling, and powder with favorable characteristics. In fact, variability in powder performance is a common issue across the pharmaceutical and dietary supplement industries. Thankfully, a number of techniques will help you under- stand and resolve problems with powders. First, however, make sure that a poor-quality tablet press or substandard compression tools are not part of the equation. You need good, reliable equipment to remediate tablet manufactur- ing issues, which typically arise unexpectedly. While understanding tablet compression is critical, the processes that precede tabletting are also very important. You must understand how particle and powder character- istics affect a tablet's quality attributes. Particle characteristics include shape, size, and size distribution, and variability in those properties can cause issues with weight, content uniformity, segregation, com- pression, and dissolution. The presence of a few overly large particles, for example, can lead to lower tablet weights because tablet dies are filled volumetrically. The large particles could also prolong dissolution because they would decrease the tablet's total surface area. The presence of overly small particles would have the inverse effect. The powder's characteristics—including its flowability and the bulk, tapped, and true density—will also have an impact on the tabletting process. True or absolute den- sity—the density once all voids are removed—can be measured using a helium pycnometer. This is a useful value because it represents the tablet's density if the com- pression event were to expel all the air between the parti- cles, including from inter-particulate and intra-particulate voids. Once you've characterized the particles and powder, decide whether direct compression—the simplest approach—is acceptable. If not, you'll need to engineer the powder, typically by dry or wet granulation. You must also understand how the powder behaves under different loading conditions. It's the only path to success in producing a robust tablet that you can scale to high-speed manufacturing. Ideally, you will learn how the material deforms to help you develop the formulation. Tablet compression process The studies described here were performed on a sin- gle-station tablet press (photo) [1]. But whether your compression machine uses a single punch and a hand- filled die or is a rotary press with a gravity or force feed- ing system, the process is similar: The material undergoes compressive forces in a confined space, causing a reduc- tion in volume. At first, the low applied pressure causes particles to rearrange and pack more closely, and porosity thus decreases. As pressure increases, the dimensions of the particles change. They either fracture into smaller discrete particles (fragmentation) or they undergo a tem- porary (elastic) or permanent (plastic) deformation into new shapes. At higher pressure, the particles that fracture could further rearrange and undergo additional deforma- tion. Tablets made from materials that undergo fragmenta- tion are typically less sensitive to weakening when pow- dered lubricants (i.e., magnesium stearate) are added. Lubricants commonly inhibit bonding between particles, but when the particles fragment, new and clean surfaces are exposed, strengthening the bond. Particles that frag- ment are also less sensitive to the speed of the compres- sion event. Materials that undergo plastic deformation are known for creating high-strength compacts at relatively low applied pressures, which stems from the greater num- ber of inter-particulate contact points during the defor- mation process. That strength, however, may decrease when lubricants are added and when the rate of compres- sion increases. Elastic deformation refers to a particle's partial or full recovery to its original shape after compres- sion loading ceases. Time-dependent elastic recovery is called viscoelasticity, and the factors that influence com- pression time are press speed, turret velocity, compres- sion roller size, and punch head dimensions. Tablet compression studies To conduct a compression study, select the tablet's tar- get weight and don't change it. Next, collect samples of tablets made at different compaction forces (low to high) and measure their thickness, weight, breaking force A single-station tablet press for conducting compression studies [1] 20 September 2016 Tablets & Capsules

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